1. Field of the Invention
The present invention relates to a system for converting food waste into fuel, and more particularly, to a system and a method for converting food waste into fuel through thermal decomposition by transferring the food waste, which is an organic waste, in a thermal decomposition reactor to pass through a region in which sunlight is concentrated by a solar concentrator.
2. Discussion of Related Art
Due to the depletion of fossil fuels, interest in the development of renewable energy technology is globally increasing, and in Korea, mandated low-carbon systems including introduction of the renewable energy portfolio standard are being developed, and as sea disposal is overall prohibited from 2013 with the implementation of the Marine Technology Management Act, development of a new plant capable of treating food waste, human excreta, etc. is required.
Food waste is food garbage disposed of from homes or restaurants, and accounts for approximately 30% of household waste along with an improved quality of the life. A food waste disposal rate in Korea has continuously increased 3% per year from 14,500 m3/day in 2007 to 17,100 m3/day in 2012. Accordingly, the annual economic loss caused by the disposed of food is 18 trillion won.
Such food waste is an organic material having a water content of 80 to 90%, and can be used as a substrate for producing feed, compost or biogas, and the feed produced from the food waste can be used for livestock. However, due to the uncertainty in demand and supply, the possibility of generating a disease in livestock, and incorporation of foreign substances, such feed can directly and indirectly damage livestock, and particularly, there is a problem in that the consumer is limited.
In addition, when left without any treatment, the food waste causes second environmental pollution due to a leachate, that is, soil acidification and an odor, and therefore the treatment of the food waste is, environmentally, an important issue. As a method of treating such food waste, incineration using an incinerator, burying in a predetermined landfill or recycling into feed or compost may be used.
However, the incineration of food waste is accompanied by incinerating costs and serious environmental problems caused by an environmentally harmful material such as a dioxin generated from incineration and an odor. In addition, the burying in a predetermined landfill is not a preferable method in Korea which has a small landmass and high population density, this is because soil or underground water is polluted due to the leachate generated from the buried food waste and thus a broad landfill for water reclamation is needed.
However, recently, food waste, which is an organic waste, has been reevaluated as a resource, and thus organic waste recycling is in the limelight.
As prior art relating to recycling of an organic waste, U.S. Patent Publication No. 2010-237291, entitled “Systems and Methods for Solar-Thermal Gasification of Biomass” is disclosed, and will be described with reference to FIGS. 1A and 1B.
FIGS. 1A and 1B are diagrams illustrating a structure of a solar tower according to the conventional art, in which FIG. 1A shows a structure of a solar tower, and FIG. 1B is a diagram for explaining a concept of gasification.
Referring to FIG. 1A, the solar tower 10 according to the conventional art is provided to gasify a biomass using high-temperature concentrated solar radiant heat, and includes a plurality of concentrators 12, a concentration field 14 and a reactor 16, and as shown in FIG. 1B, a biomass powder is passed in a state of being mixed with a carrier medium and is gasified by the concentrated solar radiant heat, and a wall of each tube in the reactor 16 may be formed of a transparent material to facilitate transfer of radiant heat.
The solar tower 10 according to the conventional art easily ensures a high temperature and has high efficiency since thermal conversion does not occur, but needs a high cost to construct the plurality of solar concentrators 12 and the solar tower 10. The above disadvantage can be solved by depositing a separate reactor 16 to correspond to each solar concentrator 12, and an organic waste is provided to each reactor 16 in an amount that can be treated by a single concentrator.
Further specifically examining the tradeoff when the structure of the solar tower 10 according to the conventional art is used, as the advantage, since equipment for converting solar energy into electricity or heat is not used, an energy utilization rate is high, and since sunlight concentrated from the plurality of solar concentrators 120 disposed in the concentration field 14, it is easy to ensure a high temperature for gasification. In addition, since it is easy to ensure a high temperature, a large amount of biomass can be gasified within a relatively fast time and thus a fuel can be stably supplied.
However, the solar tower 10 according to the conventional art needs a wide space to install the plurality of solar concentrators 120. In addition, the equipment and energy to transfer the biomass to the reactor 16 disposed at a front end of the solar tower 10 with a considerable height are needed. In addition, to facilitate the transfer, the biomass is formed in a powder, and in some cases, a separate carrier medium (vapor) is needed. In addition, a part of the radiant energy remains unutilized and is dispersed to the surroundings.
Meanwhile, as another prior art, International Application Publication No. WO2010-110772, entitled “Solar-Based Power Generator” is disclosed, which will be described with reference to FIG. 2.
FIG. 2 is a diagram illustrating a configuration in which one lens (solar concentrator) corresponds to one reactor in the solar-based power generator according to the conventional art.
Referring to FIG. 2, the solar-based power generator 20 according to the conventional art is a system for generating available power from water 24 by driving a turbine by gasifying and converting an organic material in a sewage system into steam through concentration of solar energy, and includes a base 23, at least one side wall 25 and a reactor 22 including an open upper portion. Here, one lens (solar concentrator) is configured to correspond to one reactor 22, and in this case, the sunlight concentrated by the lens 26 induces thermal decomposition of an organic material included in sewage around a focal point, driving of a steam turbine using steam generated herein, and driving of a gas turbine using methane generated thereby to generate electricity.
The solar-based power generator 20 according to the conventional art has an advantage of a low cost, and a disadvantage in that thermal decomposition at a high temperature only takes place at a focal point of the lens 16. More specifically examining the tradeoff when such a structure in which one lens (solar concentrator) corresponds to one reactor is used, the advantage is a high energy utilization rate obtained because equipment for converting solar energy into electricity or heat is not used. In addition, since sunlight is concentrated using a lens 26, a separate space for installing a reflective mirror is not necessary. In addition, since sunlight is concentrated using the lens 26, a high structure such as the conventional solar tower is not necessary. In addition, since the biomass is decomposed in a space inside the enclosed reactor 22, solar energy incident to the reactor 22 through the lens 26 can be used maximally.
However, in the solar-based power generator 20 according to the conventional art, a high temperature is generated only in a region in which light is concentrated by the lens 26, thermal decomposition or vapor generation is carried out, and a high temperature necessary for thermal decomposition or vapor generation is not generated in a different region.